This invention relates generally to packet data communication systems, and, in particular, to a method and apparatus for paging a communication unit in a packet data communication system.
Packet data communication systems are known in both the land mobile and cellular environments. In the land mobile environment, the packet data system includes a packet router, a central controller, a plurality of base sites, and a plurality of communication units (e.g., mobile radios or portable radios). In a typical land mobile data packet transmission, the packet router provides a data packet from a land user to the central controller, the central controller provides the data packet to the base site serving the communication unit, and the base site transmits the data packet.
Prior to the transmission of the data packet, the communication unit is typically paged by the serving base site. In response to receiving a paging message, the communication unit transmits an acknowledgment and the serving base site, in response to receiving the acknowledgment, transmits the data packet. However, for a variety of reasons, such as the communication unit being active in another service at the time of the page (such as being engaged in an interconnect call), or being out of radio frequency coverage, such as being in a tunnel or deep in a building in a coverage area of the serving base site, or having a dead battery, the communication unit might not respond to the paging message. In the event that the communication unit fails to acknowledge receipt of the paging message, the serving base site typically retransmits the paging message after the expiration of a predetermined time period. The communication system continues to page the communication unit by retransmitting the paging message after each repeated expiration of a constant time interval until either the base site receives an acknowledgment or until a maximum number of retransmissions have occurred. If the communication unit fails to respond after the maximum number of retransmissions, the communication system assumes that efforts to communicate with the communication unit have failed and the data packet is deleted from the system.
The problem with this paging mechanism is that it is inefficient and expensive. Radio frequency communication resources, such as a time slot of a radio frequency carrier, are limited. Each paging message occupies a radio frequency communication resource, and repeated transmittals of paging messages intended for one communication unit blocks alternative uses of the communication resource, such as the paging of other communication units. In turn, system capacity is reduced.
Therefore a need exists for a method and apparatus for paging a communication unit in a packet data communication system that will reduce the number of unsuccessful pages and increase the efficiency of radio frequency communication resource utilization.